man3/atan.3

   1 .\" Copyright 1993 David Metcalfe (david@prism.demon.co.uk)
   2 .\" and Copyright 2008, Linux Foundation, written by Michael Kerrisk
   3 .\"     <mtk.manpages@gmail.com>
   4 .\"
   5 .\" SPDX-License-Identifier: Linux-man-pages-copyleft
   6 .\"
   7 .\" References consulted:
   8 .\"     Linux libc source code
   9 .\"     Lewine's _POSIX Programmer's Guide_ (O'Reilly & Associates, 1991)
  10 .\"     386BSD man pages
  11 .\" Modified 1993-07-24 by Rik Faith (faith@cs.unc.edu)
  12 .\" Modified 2002-07-27 by Walter Harms
  13 .\"     (walter.harms@informatik.uni-oldenburg.de)
  14 .\"
  15 .TH atan 3 (date) "Linux man-pages (unreleased)"
  16 .SH NAME
  17 atan, atanf, atanl \- arc tangent function
  18 .SH LIBRARY
  19 Math library
  20 .RI ( libm ", " \-lm )
  21 .SH SYNOPSIS
  22 .nf
  23 .B #include <math.h>
  24 .PP
  25 .BI "double atan(double " x );
  26 .BI "float atanf(float " x );
  27 .BI "long double atanl(long double " x );
  28 .PP
  29 .fi
  30 .RS -4
  31 Feature Test Macro Requirements for glibc (see
  32 .BR feature_test_macros (7)):
  33 .RE
  34 .PP
  35 .BR atanf (),
  36 .BR atanl ():
  37 .nf
  38     _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L
  39         || /* Since glibc 2.19: */ _DEFAULT_SOURCE
  40         || /* Glibc <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
  41 .fi
  42 .SH DESCRIPTION
  43 These functions calculate the principal value of the arc tangent of
  44 .IR x ;
  45 that is the value whose tangent is
  46 .IR x .
  47 .SH RETURN VALUE
  48 On success, these functions return the principal value of the arc tangent of
  49 .I x
  50 in radians; the return value is in the range [\-pi/2,\ pi/2].
  51 .PP
  52 If
  53 .I x
  54 is a NaN, a NaN is returned.
  55 .PP
  56 If
  57 .I x
  58 is +0 (\-0),
  59 +0 (\-0) is returned.
  60 .PP
  61 If
  62 .I x
  63 is positive infinity (negative infinity), +pi/2 (\-pi/2) is returned.
  64 .\"
  65 .\" POSIX.1-2001 documents an optional range error for subnormal x;
  66 .\" glibc 2.8 does not do this.
  67 .SH ERRORS
  68 No errors occur.
  69 .SH ATTRIBUTES
  70 For an explanation of the terms used in this section, see
  71 .BR attributes (7).
  72 .ad l
  73 .nh
  74 .TS
  75 allbox;
  76 lbx lb lb
  77 l l l.
  78 Interface       Attribute       Value
  79 T{
  80 .BR atan (),
  81 .BR atanf (),
  82 .BR atanl ()
  83 T}      Thread safety   MT-Safe
  84 .TE
  85 .hy
  86 .ad
  87 .sp 1
  88 .SH STANDARDS
  89 C99, POSIX.1-2001, POSIX.1-2008.
  90 .PP
  91 The variant returning
  92 .I double
  93 also conforms to
  94 SVr4, 4.3BSD, C89.
  95 .SH SEE ALSO
  96 .BR acos (3),
  97 .BR asin (3),
  98 .BR atan2 (3),
  99 .BR carg (3),
 100 .BR catan (3),
 101 .BR cos (3),
 102 .BR sin (3),
 103 .BR tan (3)